Hydraulic fracturing increases fluid (e.g., hydrocarbons, and the like) flow from a subterranean zone by creating new fractures and facilitating connectivity of the existing pores and natural channels contained in the subterranean zone. Hydraulic fracturing is a process by which cracks or fractures in the subterranean zone are created by pumping a fracturing fluid at a pressure that exceeds the parting pressure of the rock. The fracturing fluid creates or enlarges fractures in the subterranean zone and a particulate proppant material suspended in the fracturing fluid may be pumped into the created fracture. This process is also known as “frac-packing”. The created fracture continues to grow as more fluid and proppant are introduced into the formation.
The proppants remain in the fractures in the form of a permeable “pack” that serves to hold open or “prop” the fractures open. After placement of the proppant materials, the fracturing fluid may be “broken” and recovered by using a breaker or a delayed breaker system to facilitate a reduction in the viscosity of the fracturing fluid. The reduction in fluid viscosity along with fluid leak-off from the created fracture into permeable areas of the formation allows for the fracture to close on the proppants following the treatment. By maintaining the fracture open, the proppants provide a highly conductive pathway for hydrocarbons and/or other formation fluids to flow into the borehole.
Slickwater fracturing is a type of treatment used in the stimulation of unconventional formations. Due to extremely low formation permeability, fluid leak-off is normally not of concern. During the slickwater hydraulic fracturing process, the pumping rate is generally very high to help facilitate the transport of proppants into the formation in conjunction with the use of the low viscosity fluid. At such fluid velocities the proppants in the fracturing fluids can be very abrasive, leading to reduced service life for fracturing equipment. In addition, friction between various components of the fracturing equipment can produce wear of the equipment. It is therefore desirable to reduce the wear on the equipment during fracturing. Guar is often used to increase the viscosity in fracturing fluids to reduce the amount of wear. Large amounts of guar in the form of a linear gel (non-crosslinked) are employed for this purpose.
A significant proportion of the total guar used in fracturing fluid operations is in the form of crosslinked fracturing fluids. For oil formations, in order to obtain the desired fracture width, higher viscosity fracturing fluids are employed. Consequently, higher loading of proppants are used to suitably prop open the relatively wide fractures. Fluids with low viscosity typically lack sufficient viscosity to carry such amounts of proppants, especially at high temperatures. Due to the costs associated with guar, it is not economical to obtain the desired high viscosity by simply increasing the concentration of the guar polymer. Overly concentrated guar fracturing fluids lead to adverse effects for the formation and proppant pack, i.e., formation or proppant pack damage, offsetting the benefit brought by the fracturing process. Thus, crosslinkers are widely used to promote crosslinking of the guar or guar-derived polymer by forming a three-dimensional (3D) network. The crosslinking agent increases the viscosity of the fracturing fluid such that the fracturing fluid has sufficient strength and viscosity to create or enlarge fractures and/or to carry the proppants during the course of the fracturing process, even at elevated temperatures. The recovery of the fracturing fluid is accomplished by using a breaker or a delayed breaker system to “break” the crosslinked guar polymers and reduce the viscosity of the fracturing fluid.
As a naturally occurring material, guar is a limited natural resource, the demand for which has increased greatly in recent years. In addition to significant supply limitations, guar-based fracturing fluids are also limited by other significant disadvantages, including but not limited to, the hydration limitations of the guar polymer, formation damage, i.e., undesirable coating of proppant materials and/or formation surfaces with the guar polymer or residue, and instability of the guar polymer at elevated temperatures in certain types of fracturing applications.
It is therefore desirable to provide an alternative to guar-based fracturing fluids, which solves one or more of the above problems associated with these guar-based fracturing fluids. It is also desirable to provide an alternative to guar-based fracturing fluids whereby the decomposition or the breaking of labile linkages therein can be facilitated, thereby lowering the viscosity and allowing for removal of the fracturing fluid.